Turbine rotor cooling mechanism

ABSTRACT

A turbine rotor cooling mechanism of a doubleflow type multistage axial-flow turbine for cooling a rotor portion between first stage wheel discs, which is subjected to the hottest gas, with relatively cool gas. The pressure in the first stage outlet on one side of the rotor portion is designed to be slightly different from that on the other side, between the first stage wheel discs a first stage nozzle ring is positioned to define an annular space surrounding the rotor portion and in the discs, holes connecting the outlet sides thereof into the annular space are formed respectively, whereby the low-temperature gas leaving the first stage on the side, on which the pressure in the outlet of the first stage is higher than that on the other side, flows through the holes formed in the disc of the side into the annular space surrounding the rotor portion and then flows out through the holes formed in the other disc so as to cool the highest temperature portion between the first stages.

United States Patent 1191 Sohma TURBINE ROTOR COOLING MECHANISM PrimaryExaminer-C. J. Husar [75] Inventor, Akio Sohma, Hitachi Japan Attorney,Agent, or FirmCraig and Antonelli [73] Assignee: Hitachi, Ltd., Tokyo,Japan 57] ABSTRACT [22] Filed: Apr. 25, 1973 A turbine rotor coolingmechanism of a doubleflow type multi-stage axial-flow turbine forcooling a rotor [21] Appl' 354466 portion between first stage wheeldiscs, which is subjected to the hottest gas, with relatively cool gas.The [30] Foreign A li ati P i it D t pressure in the first stage outleton one side of the Apr. 26, 1972 Japan 47-41327 rotor Portion isdesigned to be Slightly different from that on the other side, betweenthe first stage wheel 52 US. Cl 415/103, 415/52 415/178 discs a firstStage nozzle ring is Positioned to define 415/186 annular spacesurrounding the rotor portion and in the 51 Int. Cl. F0ld 3/02 discs,hles connecting the Outlet Sides thereof into 58 Field of Search 415/52,102, 103, 172 the annular Space are formed respectively whereby 415/1786 the low-temperature gas'leaving the first stage on the side, on whichthe pressure in the outlet of the first 56 Refe c C-ted stage is higherthan that on the other side, flows 1 UNITED gfz ILATENTS through theholes formed in the disc of the side into the annular space surroundingthe rotor portion and 2,552,239 5/l95l Warren 415/180 then fl outthrough the holes formed i the other 5 5222;: disc so as to cool thehighest temperature portion be- 3I429I557 2/1969 Brandon et a1. 415/172twee" the first Stages" 6 Claims, 2 Drawing Figures 1 TURBINE ROTORCOOLING MECHANISM BACKGROUND OF THE INVENTION This invention relates toa cooling mechanism for cooling rotors in a compressive fluid turbine,particularly a steam turbine, and more particularly to such rotorcooling mechanism for a double-flow type multistage axial-flow turbine.

In the following specification, the present invention will be describedby way of an embodiment where it was adapted to a reheating cyclic steamturbine, but it should be understood that the present invention is notlimited to such steam turbines but can as well be applied to otherordinary types of gas turbines.

Generally, in a compressive fluid turbine, it is tried to raise to themaximum the temperature of the fluid at the turbine inlet so as toobtain highest heat efficiency, but such high fluid temperature demandsuse of costly heat-resisting material for composing the parts exposed tosuch high temperature, resulting in elevated manufacturing cost.Therefore, it is usually attempted to cool the high temperature portionswith a cooling medium to allow use of ordinary non-expensive material.

Recently, the reheating cycle system is widely employed inlarge-capacity steam turbines, and there is a tendency that the mainsteam temperature as well as reheating steam temperature are more andmore elevated for obtaining high heat efficiency.

For the intermediate pressure turbine in such reheating cyclic steamturbines, it is often required to cool the rotors, because the lowtemperature exhaust steam from the high pressure turbine is overheatedto an extremely high temperature (for example 566 C) by a reheater ofthe boiler and such overheated steam flows into the intermediatepressure turbine.

In the large-capacity reheating cyclic steam turbines, a double-flowsystem is employed in the inten'nediate pressure section where turbineblades are provided usually in multiple stages respectively on bothsides of the steam inlet. As the highest temperature steam is supplyedon the rotor portion sandwitched between the first stage wheel discs onthe both sides and the highest temperature is developed on the rotorportion, it was required to provide a cooling means in this portion.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide a cooling mechanism for cooling the rotor portion disposedadjacent the first stage of such double-flow type multistage axial-flowturbine where the highest temperature is developed, said coolingmechanism being simple in arrangement and able to provide sure andpositive cooling of said rotor portion.

Another object of the present invention is to provide a coolingmechanism of the type described, which causes no decline of normalturbine performance.

In a double-flow turbine, the operative steam is separated into twoflows in the right and left directions, which are respectively passedthrough multiple-stages. In the invention of the application, steamleaving the first stage is used to cool the rotor portion developed tothe highest temperature. For this purpose, first stages on both sidesare so designed that a steam pressure in a first stage outlet on oneside will be slightly different from that on the other side. Also, astationary ring member is positioned between the first stage wheel discsof the both side and surrounding the rotor portion to define an annularspace. The wheel discs in said both right and left side assemblies ofthe first stage are formed with steam flowing holes arranged such thatthe low temperature steam leaving the first stage on one side will beflown into the annular space to cool the highest temperature portionbetween the first stages on both side, and then flown out the annularspace into the first stage outlet side on the other side. Thus, if thefirst stage of a double-flow turbine is arranged such that the pressureat the stage outlet on, for example, the right side will be lower thanthe pressure at the stage outlet on the left side, the steam leaving thefirst stage on the left side will be flown toward the first stage outleton the right side through the steam flowing holes formed in therespective wheel discs and the annular space surrounding the highesttemperature rotor portion, thereby cooling the rotor portion locatedadjacent the first stage.

The invention is now described in detail by way of'a preferredembodiment thereof with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial sectional view ofthe cooling mechanism provided adjacent the first stage of a double-flowtype multistage axial-flow turbine according to the present invention;and

FIG. 2 is a circumferential sectional view of a steam flowing hole 24provided in the mechanism of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In the drawings,reference numeral 1 indicates a turbine rotor having first stage discs 2and 3 and second stage discs 14 which are provided in both right andleft side assemblies either integrally or in assemblage. At the end ofeach of said discs are circumferentially provided moving blades asindicated by numerals 7 and 11 for the first stage and 9 and 13 for thesecond stage. In the first stage disc on the left side are formed tworows of circumferential holes 4, 24, while similar holes 28 are formedin the first stage disc on the right side. The holes 24 and 28 arepreferably perforated near the blades.

It will be also seen that the nozzles 6 and 10 correspondingrespectively to said first stage discs are circumferentially arrangedand secured in the inner casing 36 through the media of respective outerrings 37, said both nozzles being connected and secured at theirrespective inner circumferential faces by means of a first stage nozzlering 5. Extending from said first stage nozzle ring 5 are the steamsealing fins 25 and 26 and the fins define slight clearance between therespective first stage discs to operate as sealing means. At the part ofsaid nozzle ring contacted with the left-side first stage disc 3 isadditionally provided a packing 32 spaced from the sealing fin 25 andfixed on the surface of the nozzle ring 5 to ensure steam sealingbetween said disc 3 and nozzle ring 5. The holes 24 are opened betweenthe fin 25 and the packing 32. Thus, between the turbine rotor l andnozzle ring 5 is formed an annular space 20 communicated only throughthe holes and sealed portions of the first stage discs.

There are also provided the second stage nozzles 8 and 12 correspondingrespectively to the second stage moving blades 9 and 13. In order toseal between the first and second stage moving blades, steam is shut offbetween said nozzles and rotor 1 by means of diaphragms 16 and diaphragmpackings 27.

In operation of the present invention having the above-describedarrangement, high temperature steam is flown into the mechanism in thedirection of arrow 31 from a boiler reheater (not shown) and separatedinto left and right branch flows. The left branch flow passes throughthe first stage nozzle 6, moving blades 7, second stage nozzle 8 andmoving blades 9 toward the succeeding third and more number of stages(not shown). The right branch flow similarly passes through the firststage nozzle 10, moving blades 11, second stage nozzle 12 and movingblades 13 toward the succeeding third and more number of stages (notshown). If the steam temperature at the turbine inlet 15 is for instance566 C, it will have been dropped to about 530 C when leaving the firststage blades 7 or 11. The steam in the space formed between the firststage disc 2 on the right side and the first stage disc 3 on the leftside is heated by steam heat conducted from the steam chamber 15 at theturbine inlet. It may also be overheated by friction of steam on therotor surface to develop a still higher temperature. In the presentinvention, cold steam is flown into this space in the direction of arrow21 to lower the steam temperature therein to thereby keep thetemperature of the rotor l at a low level. Such flow of cold steam isintroduced in the following way. First, pressure setting is made suchthat pressure in the first stage outlet 29 on the left side will beslightly higher (usually about 3 percent higher) than pressure in thefirst stage outlet 30 on the right side. (For example, such pressuresetting may be made such that pressure in the inlet will be 160 lbs/inpressure in the left-side first stage outlet will be 90 lbs/m andpressure in the right-side first stage outlet will be 87 lbs/m Suchpressure setting involves no difficulty in practice. It may be practicedby performing the normal stage calculations independently for both rightand left sides to determine the pertinent dimensions of the respectivenozzles and moving blades on both sides. The degree of reaction at thebase of the first stage on each side is set at zero. Holes 4 and 24 areprovided in the first stage disc 3 on the left side, that is, a higherside in the first stage outlet pressure. Similar holes 28 are providedin the first stage disc 2 on the right side. Also, fins 25 and packing32 are provided at the first stage disc portion on the left side, andthe total area of said steam flowing holes and the area of the packingspace are so selected that the amount of steam passing through the holes4 will be more than 10 times the amount of steam flowing into the space20 through the packing 32. This means that the substantial portion ofcold steam flown into the space 20 passes through the holes 4. The sizesof said holes 4 and 24 are determined such that the total area of theholes 24 will be about 0.5 time the total area of the holes 4. The areapresented by the spaces formed by the fins 25 should be approximately0.4 time the total area of the holes 24. Holes 24 are designed tofacilitate flow of steam by somewhat utilizing the dynamic pressurecreated by rotation of the discs as shown in FIG. 2 wherein the inletportion of the hole 24 is cut out as shown by numeral 17 on theprogressive side thereof. Since the degree of reaction at the firststage is set at zero as mentioned before, the pressures at both inletand outlet sides are at the same level at the base of the moving blades.But as the holes 24 are designed to utilize the dynamic pressure as saidabove, the steam in the outlet 29 flows through the holes 24 to theright direction, and also because the areas of the packing or fins andthe holes are set at such relation as aforesaid, the steam from theholes 24 is divided into two portions, one portion flowing through thepacking 32 as indicated by numeral 22 and the other portion flowingtoward the base of the moving blades as indicated by numeral 23. Thus,the steam 22 flown into the space 20 through the packing 32 is all thelow temperature steam which has flown past the first stage through theholes 24, and the high temperature steam in the inlet side of the movingblades is inhibited from flowing into the space 20 due to generation ofsteam flow 23. The steam in the space 20 flows in the direction of arrow21 and then further flows along the surface of the right-side firststage disc and then through the holes 28 to leave the first stage on theright side. Fins 26 are provided to prevent the cooling steam fromleaking into the outlet portion of the nozzle 10.

In this way, the low temperature steam which has flown past the firststage of the turbine is flown into the space 20 incessantly during theturbine operation, whereby in a turbine with the inlet steam temperatureof 566 C, the temperature at this portion will be dropped to about 530C. FIG. 2 shows a portion of a hole 24 as it was cut circumferentiallyof the disc. The disc is rotated in the direction of arrow 18 with acertain peripheral velocity, so that if the portion of the hole 24 onthe outlet side 33 of the stage is cut in the manner as shown by numeral17, the steam will be partly dammed up by the hole face 35, and hencepressure is raised by the action of a part of the dynamic pressure, thatis, a slight portion of the dynamic pres sure is recovered by the steamflow 19.

In this manner, pressure of steam flowing through the holes 24 becomesslightly higher than steam pressure at the nozzle outlet of the firststage on the left side. If need be, the holes 4 may be configured justlike the holes 24 shown in FIG. 2.

While the present invention has been described by way of an embodimentwhere it was adapted to the intermediate pressure section of a steamturbine, it will be understood that this invention can as well beapplied to the other parts of the steam turbine or other types ofturbines such as gas turbines.

Also, although in the shown embodiment arrangement is made such that thesteam pressure after the first stage moving blades will be higher in theleft side than in the right side, it is possible to make such steampressure higher in the right side than in the left side with ease.

Use of the cooling mechanism according to the present invention canproduce the following excellent effects:

1. Sure and perfect cooling can be achieved with a simple mechanism. Asshown in F IG. 1, the device of the present invention is very simple inconstruction and requires little maintenance after operations. As thecooling steam flows constantly in the manner as indicated by arrow 21 inthe figure, there is no possibility that heat be accumulated in thespace 20 due to conduction of heat from the steam chamber 15 or byfriction of steam on the rotor surface, and hence cooling can beaccomplished most efficiently.

2. No drop of turbine performance is caused. The first stage assemblieson both right and left sides are of an impulse construction where thedegree of reaction at the base portion of each assembly is confined tothe minimum. In the conventional cooling systems employing negativereaction stages (such as shown in US. Pat. No. 3,429,557 to R. E.Brandon et al.), certain decline of working performance as compared withthe normal stages is unavoidable. But, no such decline of workingperformance is caused in the present invention. As is well known, if astage is designed to provide a negative reaction degree, rise ofpressure takes place in the rows of turbine blades just like acompressor, causing disorder or separation of flow on the blade surface,resulting in reduced working efficiency of the stage. According to thepresent invention, however, such is perfectly prevented by use of animpulse stage to allow as high heat performance of the turbine as in thenormal stages.

What is claimed is:

1. In a double-flow type multi-stage axial-flow turbine having firststage nozzles positioned stationarily on both sides of a steam inlet andfirst stage moving blades mounted on first stage wheel discs of a rotorto be rotatable with the rotor, a turbine rotor cooling mechanismcomprising:

first stage nozzle ring means mounting said first stage designed that aoutlet side pressure in one side of said first stage will be slightlydifferent from that in the other side.

2. A turbine rotor cooling mechanism according to claim 2, which furthercomprises;

additional sealing means provided between said first stage nozzle ringmeans and the first stage wheel disc in the side where the outlet sidepressure is higher and spaced from said sealing means on the same side;and

additional holes perforated in said first stage wheel disc and openedbetween said sealing means and said additional sealing means.

3. A turbine rotor cooling mechanism according to claim 2, wherein saidfirst stage moving blades are designed such that the degree of reactionat the base thereof will be minimized in a positive region, and saidadditional holes have cut-out portions (17) on a progressive side of aninlet portion thereof so as to pass steam or gas from the outlet side ofthe first stage therethrough by utilizing a dynamic pressure created byrotor rotation.

4. A turbine rotor cooling mechanism according to claim 2, wherein thefirst stage outlet pressure in one side is different by about 3 percentfrom that in the other side.

5. A turbine rotor cooling mechanism according to claim 2, wherein saidadditional holes perforated in the first stage wheel disc is near theblades and said holes in the other first stage wheel disc is also nearthe blades.

6. A turbine rotor cooling mechanism according to claim 2, wherein saidsealing means formed between said ring means and said wheel discs atboth ends of the ring means, comprises fins formed integrally on eithersurfaces of said ring means or said wheel discs extending to thecorresponding surfaces to define a slight clearance therebetween andsaid additional sealing means comprise packings fixed on either surfacesof said ring means or said wheel disc.

1. In a double-flow type multi-stage axial-flow turbine having firststage nozzles positioned stationarily on both sides of a steam inlet andfirst stage moving blades mounted on first stage wheel discs of a rotorto be rotatable with the rotor, a turbine rotor cooling mechanismcomprising: first stage nozzle ring means mounting said first stagenozzles on an outer surface at both ends thereof, arranged between saidfirst stage wheel discs on both sides to surround the rotor so as todifine an annular space; sealing means formed between said ring meansand said wheel discs at both ends of the ring means; and, holesperforated in said wheel discs on both sides so as to connectfluidically said annular space to outlet sides of the first stage movingblades; wherein first stage assemblies composed of said first stagenozzles and first stage moving blades are so designed that a outlet sidepressure in one side of said first stage will be slightly different fromthat in the other side.
 2. A turbine rotor cooling mechanism accordingto claim 2, which further comprises; additional sealing means providedbetween said first stage nozzle ring means and the first stage wheeldisc in the side where the outlet side pressure is higher and spacedfrom said sealing means on the same side; and additional holesperforated in said first stage wheel disc and opened between saidsealing means and said additional sealing means.
 3. A turbine rotorcooling mechanism according to claim 2, wherein said first stage movingblades are designed such that the degree of reaction at the base thereofwill be minimized in a positive region, and said additional holes havecut-out portions (17) on a progressive side of an inlet portion thereofso as to pass steam or gas from the outlet side of the first stagetherethrough by utilizing a dynamic pressure created by rotor rotation.4. A turbine rotor cooling mechanism according to claim 2, wherein thefirst stage outlet pressure in one side is different by about 3 percentfrom that in the other side.
 5. A turbine rotor cooling mechanismaccording to claim 2, wherein said additional holes perforated in thefirst stage wheel disc is near the blades and said holes in the otherfirst stage wheel disc is also near the blades.
 6. A turbine rotorcooling mechanism according to claim 2, wherein said sealing meansformed between said ring means and said wheel discs at both ends of thering means, comprises fins formed integrally on either surfaces of saidring means or said wheel discs extending to the corresponding surfacesto define a slight clearance therebetween and said additional sealingmeans comprise packings fixed on either surfaces of said ring means orsaid wheel disc.